This invention relates to a digital waveform conditioning circuit for processing a digital signal.
Recently, progress has been made in the technique of processing a digital signal. Analog signals such as audio signals are recorded after being converted into digital signals such as pulse code modulation (PCM) signals. Also, in the field of signal transmission, digital signals are processed. In this connection it will be noted that reproduced or transmitted digital signals cease to have a perfect rectangular waveform since they are deteriorated by the signal to noise (S/N) ratio or frequency characteristic of the recording or transmission system. Therefore, it is necessary to carry out waveform conditioning of the digital signals obtained in order to restore the rectangular waveform of the original signals.
A digital waveform conditioning circuit generally comprises a comparator for comparing the level of an input signal with a predetermined reference value and a holding circuit for reading an output signal from the comparator in response to a clock signal and for holding the fetched signal.
When, however, an input signal includes noise, it sometimes happens that an output signal from the comparator ceases to denote a code corresponding to that of the original rectangular signal and is decoded in the wrong audio signal. Such conditioning error is detrimental in the processing of a digital rectangular signal. Further, the rectangular waveform of a digital signal has an extremely broad frequency spectrum. Consequently, the digital signals should have a broad frequency characteristic to assure proper recording, reproducing or transmission, and also to assure that the signals are recorded, produced, or transmitted with greater density. However, the S/N ratio and frequency characteristic of the recording, reproducing, and transmission systems generally becomes less satisfactory in the higher frequency regions. When, therefore, digital signals are recorded, reproduced or transmitted with higher density, the percentage occurrence of errors tends to increase.